A retroreflective sheet structure comprises a transparent thermoplastic layer having a front light-receiving surface and a rear retroreflecting surface. Light incident on the front surface passes through the clear thermoplastic layer, impinges on the rear retroreflecting surface, and is reflected back out through the front surface in a predetermined direction (e.g., aligned with and/or parallel to the direction of incidence). In this manner, incident light can be used to illuminate markings, words, and other information in an otherwise dark environment.
The retroreflecting surface can be formed by a repeating array of retroreflective elements embossed in the thermoplastic layer. The retroreflective elements can comprise, for example, corner-cube elements which each have three flat faces arranged mutually at right angles and connected by edges which join at an apex. (See e.g., U.S. Pat. No. 1,906,655, U.S. Pat. No. 3,332,327, U.S. Pat. No. 3,541,606, U.S. Pat. No. 3,833,285, U.S. Pat. No. 3,873,184, and/or U.S. Pat. No. 3,923,378. See also, U.S. Pat. No. 6,767,102 which is assigned to the assignee of the present invention and the entire disclosure which is hereby incorporated by reference).
Over the years, retroreflective sheet structures have been incorporated into a wide range of end products including, for example, vehicle markings, highway signs, and construction barrels. In these and other applications, extended outdoor durability is important and the retroreflective sheet structure needs to withstand extended sun light exposure and other harsh environmental conditions. An expected useful life of twelve years is not considered an unreasonable requirement when a retroreflective structure is being used in a highway situation. Even in less demanding, more delicate settings, the retroreflective structure is expected to maintain its physical stability and optical reflectivity for a certain period of time (e.g., one to five years).
Typically, an end product manufacturer will receive a roll of retroreflective sheeting from an independent supplier. During the manufacture of the end product, the sheeting is unwound from the roll and separated into individual structures for integration into the end product. As such, a retroreflective sheeting supplier may be unaware of what end products its sheeting is being used in and/or where the end product is being used, especially after an extended period of time. Additionally or alternatively, an end product manufacturer having a plurality of sheeting suppliers (which is dictated by many companies' purchasing policies) may find it difficult to track the identify of the supplier whose sheeting was used in a particular end product.